The present application claims priority under 35 U.S.C. xc2xa7 119 of German Patent Application No. 199 04 576.3, filed on Feb. 4, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
The present invention relates to a press arrangement and process for treating a fibrous material web, e.g., a paper or cardboard web.
The present invention provides a press arrangement of the type generally discussed above, which also has a simple and compact design, as well as vacuum requirements and drive output that are as small as possible. In addition, closed web guidance system is possible.
Therefore, the present invention provides two shoe press rolls assigned to a central press roll, which acts as a shared counter-roll. In this way, the shoe press rolls, along with the central roll, can be arranged to form press nips that are elongated in the web travel direction. Further, the first elongated press nip, as viewed in the web travel direction, is provided with two felts.
With this design, the conventional, large suction press provided with a thick jacket can be omitted which in turn appreciably reduces the vacuum requirements. Thus, there is an overall appreciably smaller power requirement. In particular, it becomes easy to provide the web with a closed guidance system, so that the corresponding press section is particularly suitable for liners with a xe2x80x9cwhite top.xe2x80x9d By using an opposing roll assigned to the two shoe press rolls, the number of needed press rolls is also reduced to the minimum, i.e., a maximum of only three press rolls is required. Accordingly, the number of necessary press felts is also reduced, and this reduced felt consumption lowers operating costs. Operating costs are further reduced by the lower vacuum requirement for tube suction devices and by the lower power requirement.
In particular, an arrangement becomes possible in which the press forces for the most part counterbalance each other. Furthermore, there is a reduced bearing load and a reduced bending load on the roll axle, and it is possible to eliminate an inwardly supported roll, if need be, for all machine widths. The decreased energy consumption is in part due to the fact that, with only one opposing roll assigned to the shoe press rolls, the lower bearing friction lessens the amount of friction created within the press arrangement. The reduction in the number of felts thereby reduces felt reconditioning, which further reduces friction and the vacuum requirement. Losses caused by rolls that are inwardly supported are eliminated, and only a single drive outside of the given paper machine is necessary, which results in improved efficiency. When the number of employed rolls and roll types are reduced to a minimum, the number of reserve rolls needed also becomes low, which in turn has a favorable effect on investment costs. Moreover, a simpler control system becomes possible, which thereby increases operating safety. Compared to conventional multi-roll presses, the line of force is not affected by reciprocal nip forces, and camberings become largely unnecessary. It is also no longer necessary to use soft roll covers, which results in longer tool lives. A varying degree of pull on the paper is practically eliminated. Consequently, it is possible to avoid web tears within the press section. In particular, it is possible to have a simpler, lever-free, and compact support with a closed flow of force. With the elimination of press roll scrapers for paper removal, the investment and operating costs are further diminished.
The two shoe press rolls can preferably be positioned on opposite sides of the central press roll.
In an exemplary embodiment of the press arrangement according to the instant invention, each of the two elongated press nips are provided with two felts. Overall, this provides symmetrical dewatering that also affords a savings in terms of volume. In paper manufacturing, the equal-sidedness of the paper is particularly improved, so that the press arrangement can also be used for graphic papers.
In another exemplary embodiment of the press arrangement according to the invention, a total of at most three felts is provided. A felt can be guided through both elongated press nips. Only three felt treatments are therefore necessary which in turn reduces the creation of friction as well as the vacuum requirement. There is a reduced total felt consumption. Overall, a compact and cost-effective design is possible. Not only can the suction press roll be omitted, but a closed web guidance and relatively short remoistening zones are possible. Good nip dewatering is provided after each nip, which can be achieved by, e.g., centrifugal water removal.
A highly reliably transport of the web can be achieved with a closed web guidance system from the screen to the drier section, and the press arrangement practically eliminates tears in the web. Furthermore, the manual setup of the fibrous material web is eliminated, which results in a higher degree of operating safety and greater machine availability. Moreover, due to the absence of open pulls, it is practically impossible to have paper stretching and/or web tears. There are also no fluctuations in pull on the paper between the presses.
Between the two elongated press nips formed with the central press roll, the fibrous material web, along with a felt, can ideally be guided around a deflection roll preferably designed as a suction roll.
In a useful practical embodiment, a felt guided through the first elongated press nip simultaneously serves as a pick-up felt.
It is also advantageous for the fibrous material web, following the second elongated press nip, to be guided over a deflection roll in the form of a suction roll, e.g., to an adjacent drier section. Here, the fibrous material web can be conducted around the deflection roll, along with an upper felt running through the second elongated press nip, and then be removed from the upper felt by a smooth roll. As an alternative, it is possible, e.g., to guide the fibrous material web, along with a lower felt, out of the second elongated press nip and to remove it from the lower felt in the area of the deflection roll, specifically with a drying screen which wraps around the deflection roll.
The surface of the central press roll and/or the press jacket of at least one shoe press roll can be blind-bored and/or grooved in order to create a certain water storage capability. In this way, the dewatering of one or both elongated press nips can be performed at least in part by centrifuging the water through a given groove. This not only assures the optimal dewatering of the given press nip, but can enable the use of lighter press felts. Finally, improved felt conditioning via tube suction devices and spray tubes may be provided.
In certain cases it may be useful for the support devices assigned to the press shoes of the two shoe press rolls to be able to be subjected to the same pressures. Here, it will be more effective for the length of the first elongated press nip to be greater than the length of the second elongated press nip. In particular, it is possible to have equal line forces. In an alternative embodiment, the supporting device assigned to the press shoe of the first shoe press roll can be subjected to a lower pressure than the supporting device assigned to press shoe of the second shoe press roll. In this case, it will be effective for the two elongated press nips to have the same length. Here in particular, the line force of the second elongated press nip can be greater than that of the first elongated press nip.
For reasons of weight, it may be useful for the central press roll to be an inwardly supported roll and to be provided with the pressures assigned to each of the press nips.
In order to influence the felt tension between the two elongated press nips, it may be advantageous for the deflection roll to have an adjustable drive.
Accordingly, the present invention is directed to a press arrangement for treating a fibrous material web that includes two shoe press rolls and a counter-roll, associated with the two shoe press rolls, positioned to form a first and a second press nip with the two shoe press rolls. The first and the second press nip are elongated in a web travel direction. The press arrangement also includes a plurality of felts, such that two of the plurality of felts are guided through at least the first press nip.
In accordance with a feature of the invention, the two shoe press rolls may be positioned on opposite sides of the counter-roll.
According to another feature of the present invention, two of the plurality of felts may be guided through the second press nip.
According to a further feature of the invention, the plurality of felts can at most three felts.
In accordance with still another feature of the invention, the press arrangement can be a closed web guidance system.
In accordance with another feature of the invention, one of the plurality of felts may be guided through both of the first and the second press nips.
A deflection roll may be positioned such that the material web, between the first and the second press nip, is guided around the deflection roll. The deflection roll can include a suction roll, and the material web may be guided over the deflection roll by at least one of the plurality of felts.
In accordance with still another feature of the present invention, one of the plurality of felts guided through the first press nip can also arranged as a pick-up felt.
A deflection roll can be provided, such that, following the second press nip, the fibrous material web can be guided by the deflection roll. The deflection roll can include a suction roll, and the deflection roll can be arranged to guide the fibrous material web to an adjacent dryer section. A smooth roll may also be provided, and one of the plurality of felts may be arranged as an upper felt and may be guided through the second press nip. The smooth roll can be arranged to separate the material web from the upper felt. Moreover, a dryer screen that wraps around the deflection roll can be provided, and another one of the plurality of felts may be arranged as a lower felt and can be arranged to guide the fibrous material web out of the second press nip. The dryer screen may be positioned to separate the fibrous material web form the lower felt in a vicinity of the deflection roll.
The counter-roll can be at least one of blind-bored and grooved.
At least one of the counter-roll and at least one jacket of the two shoe press rolls can include at least one of at least one bore and at least one groove. Further, dewatering of the first and the second press nip may be performed at least in part by spinning off water in the at least one at least one bore and at least one groove.
In accordance with a particular feature of the instant invention, each of the two press shoe rolls can include at least one press shoe and at least one supporting device associated with the at least one press shoe, and a length of the at least one press shoe forming the first press nip may be greater than a length of the at least one press shoe forming the second press nip. A same pressure can be applied to the at least one supporting device in both of the two shoe press rolls.
According to another particular feature of the instant invention, each of the two press shoe rolls can include at least one press shoe and at least one supporting device associated with the at least one press shoe, and a length of the at least one press shoe forming the first press nip may be the same as a length of the at least one press shoe forming the second press nip. A pressure applied to the at least one supporting device adapted to form the first press nip may be lower than a pressure applied to the at least one supporting device adapted to form the second press nip.
According to another feature of the instant invention, at least one of the two shoe press rolls can include at least one of a blind-bored and grooved press jacket.
In accordance with still another feature of the present invention, the counter-roll can be an inwardly supported roll with pressures corresponding to pressures in the first and the second press nips.
According to a further feature of the invention, an aspirating deflection roll and a web-supporting aspirator may be provided. The web-supporting aspirator can be positioned between the aspirating deflection roll and the second press nip, and one of the plurality of felts can be arranged as a lower felt, so that the web-supporting aspirator is positioned to secure the fibrous material web to the lower felt. The aspirated deflection roll can have an adjustable drive. Further, the aspirated deflection roll and the adjustable drive can also be braked, whereby felt tension is increased in front of the second press nip.
In accordance with another feature of the present invention, the fibrous material web may include one of a paper web and a cardboard web. Further, the counter-roll can be arranged as a central press roll.
The present invention is also directed to a process for treating a fibrous material web in an apparatus that includes two shoe press rolls, a counter-roll, associated with the two shoe press rolls, that is positioned to form a first and a second elongated press nip in a web travel direction with the two shoe press rolls, and a plurality of felts, in which two of the plurality of felts are guided through at least the first elongated press nip. The process includes transferring the web onto a pick-up felt, where the pick-up felt is one of the two felts guided through at least the first press nip, and dewatering the web between the two felts in the first elongated press nip.
In accordance with a feature of the invention, the apparatus includes two of the plurality of felts being guided through the second elongated press nip, and the process may further include dewatering the web between the two felts in the second elongated press nip. Further, the process can include guiding the fibrous material web through the first and second elongated press nips with a same felt.
According to another feature of the invention, each shoe press roll includes at least one press shoe and at least one supporting device associated with each at least one press shoe, and a length of the at least one press shoe forming the first elongated press nip is greater than a length of the at least one press shoe forming the second elongated press nip. In this manner, the process may further include applying a same pressure to the at least one supporting device in both of the two shoe press rolls.
In accordance with still another feature of the instant invention, each shoe press roll includes at least one press shoe and at least one supporting device associated with each at least one press shoe, and a length of the at least one press shoe forming the first elongated press nip is the same as a length the at least one press shoe forming the second elongated press nip. In this manner, the process may further include applying a pressure to the at least one supporting device adapted to form the first press nip that is lower than a pressure applied to the at least one supporting device adapted to form the second press nip.
According to yet another feature of the present invention, the process can further include adjusting a felt tension prior to the second elongated press nip.
The present invention is also directed to a press arrangement for treating a fibrous material web including two shoe press rolls and a counter-roll, associated with the two shoe press rolls, positioned to form a first and a second press nip with the two shoe press rolls. The first and the second press nip are elongated in a web travel direction, and the counter-roll is arranged as a central press roll. Three felts, in which two of the three felts are guided through at least the first nip, in which two of the three felts are guided through the second press nip, and in which one of the three felts is guided through both of the first and the second press nips. The two shoe press rolls are positioned on opposite sides of the counter-roll, and the press arrangement is a closed web guidance system.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.